This chapter covers the anatomy of the heart, cardiac circulation, cardiac conduction, the cardiac cycle, the vascular system, cardiovascular assessment, and abnormal findings.
By the end of this lecture, you should be able to:
Describe the location and basic structure of the heart.
Identify the four heart chambers.
Explain the purpose of the four heart valves.
Trace blood through the heart, lungs, and body.
Distinguish oxygenated from deoxygenated blood.
Explain systole and diastole.
Describe the electrical conduction system.
Explain heart rate, stroke volume, and cardiac output.
Understand preload, afterload, and contractility.
Connect cardiovascular physiology to common assessment findings.
Recognize cardiovascular warning signs requiring immediate attention
You are assessing a 73-year-old patient admitted because of worsening fatigue.
The patient says:
“I become short of breath just walking to the bathroom.”
Your assessment reveals:
Heart rate: 112/min
Blood pressure: 96/60 mmHg
Respiratory rate: 26/min
Cool hands and feet
Weak peripheral pulses
Bilateral ankle edema
Crackles at both lung bases
Urine output lower than usual
These findings involve several body systems:
Lungs
Skin
Kidneys
Peripheral circulation
Heart
However, they may all arise from one central problem:
The heart may not be pumping enough blood forward.
When cardiac output falls:
The brain may receive less blood, causing confusion.
The kidneys may receive less blood, decreasing urine output.
The skin may become cool and pale.
The pulse may become weak.
Blood may back up into the lungs, causing crackles.
Blood may back up into the veins, causing edema.
This is why cardiovascular assessment requires you to examine the entire patient.
The cardiovascular system consists primarily of:
The heart
Arteries
Arterioles
Capillaries
Venules
Veins
Blood
Its major job is transportation.
It transports:
Oxygen
Carbon dioxide
Nutrients
Hormones
Immune cells
Waste products
Heat
The cardiovascular system connects every organ.
If circulation stops, every organ is affected.
The heart lies in the chest within the mediastinum.
It is positioned:
Behind the sternum
Between the lungs
Above the diaphragm
Mostly to the left of the body’s midline
The upper broad portion is called the:
Base
The pointed lower portion is called the:
Apex
The apex points:
Downward
Forward
To the left
In many adults, the apical impulse is located near the:
Fifth left intercostal space at or near the midclavicular line
This landmark becomes important during palpation and auscultation.
The heart is surrounded by a protective sac called the:
Pericardium
It has layers that contain a small amount of lubricating fluid.
This fluid reduces friction as the heart beats.
When the pericardium becomes inflamed, its surfaces may rub together and produce a scratchy sound called a:
Pericardial friction rub
The textbook describes this as a grating or leathery sound associated with pericardial inflammation.
The heart is divided into four chambers:
Right atrium
Right ventricle
Left atrium
Left ventricle
The atria are the upper receiving chambers.
The ventricles are the lower pumping chambers.
The right atrium receives deoxygenated blood returning from the body.
Blood enters through:
Superior vena cava
Inferior vena cava
Coronary sinus
The superior vena cava brings blood from the:
Head
Neck
Upper extremities
Upper chest
The inferior vena cava brings blood from the:
Abdomen
Pelvis
Lower extremities
The coronary sinus returns blood from the heart muscle itself.
Blood moves from the right atrium through the tricuspid valve into the right ventricle.
The right ventricle pumps blood:
Through the pulmonic valve
Into the pulmonary artery
Toward the lungs
The right ventricle pumps against relatively low pressure because the lungs are close to the heart.
Its wall is therefore thinner than the left ventricular wall.
The left atrium receives oxygenated blood from the lungs.
Blood returns through the:
Pulmonary veins
This is an important exception:
Most veins carry deoxygenated blood.
Pulmonary veins carry oxygenated blood.
Blood moves from the left atrium through the mitral valve into the left ventricle.
The left ventricle pumps blood:
Through the aortic valve
Into the aorta
Throughout the entire body
The left ventricle has the thickest muscular wall because it must generate enough pressure to move blood through systemic circulation.
Atria receive. Ventricles eject.
Right atrium receives from the body.
Right ventricle ejects toward the lungs.
Left atrium receives from the lungs.
Left ventricle ejects toward the body.
Valves keep blood moving in one direction.
They open and close according to pressure differences.
The four valves are divided into:
Atrioventricular valves
Semilunar valves
These valves lie between the atria and ventricles.
Located between:
Right atrium
Right ventricle
It has three leaflets.
Located between:
Left atrium
Left ventricle
It has two leaflets.
It is also called the:
Bicuspid valve
These lie between the ventricles and the major arteries.
Located between:
Right ventricle
Pulmonary artery
Located between:
Left ventricle
Aorta
Use:
Try Pulling My Aorta
Tricuspid
Pulmonic
Mitral
Aortic
This follows the basic direction of blood through the heart beginning on the right side.
If a valve does not open completely:
Stenosis
Blood must move through a narrowed opening.
This creates resistance and turbulence.
If a valve does not close properly:
Regurgitation or insufficiency
Blood leaks backward.
Both problems may produce murmurs.
A murmur is the sound of turbulent blood flow—not a disease by itself.
Open the visual:
heart_blood_flow.png
Follow this sequence slowly.
Deoxygenated blood enters:
Superior vena cava
Inferior vena cava
Then flows into the:
Right atrium
Blood passes through the:
Tricuspid valve
Then enters the:
Right ventricle
Blood passes through the:
Pulmonic valve
Then enters the:
Pulmonary artery
The pulmonary artery carries blood to the lungs.
This is another important exception:
Most arteries carry oxygenated blood.
The pulmonary artery carries deoxygenated blood.
In the pulmonary capillaries:
Carbon dioxide leaves the blood.
Oxygen enters the blood.
Oxygenated blood returns through:
Pulmonary veins
Then enters the:
Left atrium
Blood passes through the:
Mitral valve
Then enters the:
Left ventricle
Blood passes through the:
Aortic valve
Then enters the:
Aorta
From the aorta, it travels throughout the body.
Memorize this only after understanding it:
Body → vena cavae → right atrium → tricuspid valve → right ventricle → pulmonic valve → pulmonary artery → lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → body
Right heart goes to respiration.
Left heart goes to life.
The right side sends blood to the lungs.
The left side sends blood to the body.
Understanding circulation helps explain heart failure findings.
The left ventricle cannot pump blood forward effectively.
Blood backs up toward:
The lungs
Possible findings:
Shortness of breath
Orthopnea
Crackles
Cough
Low oxygen saturation
Pulmonary edema
Fatigue
Memory:
Left backs into the lungs.
The right ventricle cannot pump blood effectively toward the lungs.
Blood backs up into:
The systemic veins
Possible findings:
Jugular venous distention
Peripheral edema
Weight gain
Liver enlargement
Ascites
Dependent swelling
Memory:
Right backs into the rest of the body.
Many patients eventually develop findings from both sides.
Path:
Right ventricle → lungs → left atrium
Purpose:
Remove carbon dioxide
Add oxygen
This is a relatively low-pressure system.
Path:
Left ventricle → body → right atrium
Purpose:
Deliver oxygen and nutrients
Remove waste products
This requires higher pressure because blood must travel throughout the body.
The heart muscle needs its own blood supply.
The coronary arteries branch from the beginning of the aorta.
They supply oxygen to the myocardium.
When a coronary artery becomes blocked:
Myocardial tissue becomes ischemic.
If prolonged, myocardial infarction may occur.
Pumping ability may decrease.
Dangerous electrical rhythms may develop.
This explains why coronary circulation is essential even though the heart chambers contain blood.
Blood inside the chambers does not directly nourish most of the heart muscle.
The heart must contract in a coordinated sequence.
Atria contract first.
Ventricles contract afterward.
This coordination comes from the electrical conduction system.
Open the visual:
heart_conduction_pathway.png
The textbook introduces cardiac conduction as part of the physiology of the heart.
The sinoatrial node is called the:
Natural pacemaker of the heart
It is located in the right atrium.
It normally initiates each heartbeat.
The impulse spreads through both atria and causes:
Atrial contraction
A normal rhythm originating from the SA node is called:
Normal sinus rhythm
The impulse reaches the:
AV node
The AV node delays the impulse briefly.
Why?
The delay gives the atria enough time to empty blood into the ventricles before the ventricles contract.
Without this delay, atrial and ventricular contraction would be poorly coordinated.
After the AV node, the impulse enters the:
Bundle of His
This structure carries the electrical signal into the interventricular septum.
The signal divides into:
Right bundle branch
Left bundle branch
These carry the impulse toward each ventricle.
The impulse spreads through the ventricular muscle using the:
Purkinje fibers
This causes the ventricles to contract from the lower regions upward.
That direction helps push blood toward:
Pulmonary artery
Aorta
SA node → atria → AV node → Bundle of His → right and left bundle branches → Purkinje fibers → ventricles
Start, delay, divide, distribute.
SA node starts.
AV node delays.
Bundle branches divide.
Purkinje fibers distribute.
If the SA node fails, other cardiac cells may create impulses.
However, backup pacemakers usually fire more slowly.
If electrical conduction is blocked:
Heart rate may slow.
Atria and ventricles may lose coordination.
Cardiac output may fall.
Syncope or weakness may occur.
The cardiac cycle includes all events occurring during one heartbeat.
It has two major phases:
Diastole
Systole
During diastole:
Ventricles relax.
Ventricular pressure falls.
AV valves open.
Ventricles fill with blood.
Think:
Diastole = filling.
Much of ventricular filling is passive.
Near the end of diastole, the atria contract and add the final amount of blood.
This is sometimes called the:
Atrial kick
The atrial kick becomes especially important when ventricles are stiff or heart rate is high.
During systole:
Ventricles contract.
AV valves close.
Ventricular pressure rises.
Pulmonic and aortic valves open.
Blood is ejected.
Think:
Systole = squeezing.
Heart sounds are produced primarily by valve closure and associated vibrations.
S1 occurs when the:
Mitral valve closes.
Tricuspid valve closes.
It marks the beginning of ventricular systole.
S1 is often described as:
“Lub”
It is loudest near the apex.
S2 occurs when the:
Aortic valve closes.
Pulmonic valve closes.
It marks the end of systole and beginning of diastole.
S2 is often described as:
“Dub”
It is loudest near the base.
S1: AV valves shut.
S2: Semilunar valves shut.
Cardiac output is the amount of blood the heart pumps each minute.
Formula:
Cardiac Output = Heart Rate × Stroke Volume
Written:
CO = HR × SV
Heart rate is the number of beats per minute.
A higher heart rate may initially increase cardiac output.
However, if the heart beats too quickly:
Filling time decreases.
Coronary perfusion may decrease.
Stroke volume may fall.
Cardiac output may eventually decline.
A very slow heart rate may also lower cardiac output because too few beats occur each minute.
Stroke volume is the amount of blood ejected by one ventricle during one contraction.
Stroke volume depends mainly on:
Preload
Contractility
Afterload
Preload refers to the amount of stretch in the ventricular muscle before contraction.
It is related to how much blood fills the ventricle at the end of diastole.
Think:
Preload = filling before pumping.
Higher venous return usually increases preload.
Examples that may increase preload:
Fluid overload
Kidney failure
Excess intravenous fluids
Heart failure with volume retention
Examples that may reduce preload:
Hemorrhage
Dehydration
Diuretics
Severe vomiting
Venodilation
Within limits:
More filling produces a stronger contraction.
Imagine stretching a rubber band.
A moderate stretch allows stronger recoil.
However, overstretching weak or failing heart muscle can worsen congestion rather than improve output.
Contractility is the heart muscle’s intrinsic ability to contract.
Think:
Contractility = squeezing strength.
Contractility may increase with:
Sympathetic stimulation
Certain medications
Increased circulating catecholamines
It may decrease with:
Myocardial infarction
Severe hypoxemia
Acidosis
Cardiomyopathy
Some medications
Reduced contractility means less blood is ejected with each beat.
Afterload is the resistance the ventricle must overcome to eject blood.
Think:
Afterload = pressure the heart pumps against.
For the left ventricle, afterload is strongly influenced by:
Systemic vascular resistance
Aortic pressure
Aortic valve narrowing
High blood pressure increases left ventricular afterload.
The heart must work harder to pump against that pressure.
Over time, the ventricular muscle may thicken.
Imagine pushing open a door.
Preload: How far you pull your arm back before pushing.
Contractility: How strongly your muscles push.
Afterload: How heavy or resistant the door is.
Stroke volume: How much the door moves with one push.
Cardiac output: How much total movement occurs over one minute.
Blood pressure is created by the interaction of:
Cardiac output
Blood volume
Vascular resistance
A simplified relationship is:
Blood pressure depends on cardiac output × systemic vascular resistance
Blood pressure alone does not guarantee adequate perfusion.
A patient may have an acceptable blood pressure yet still have:
Poor skin perfusion
Reduced urine output
Altered mental status
Weak pulses
Always assess the patient, not only the number.
Possible findings include:
Hypotension
Tachycardia or bradycardia
Weak pulses
Cool skin
Pallor
Delayed capillary refill
Confusion
Dizziness
Fatigue
Decreased urine output
Chest pain
Shortness of breath
The kidneys require adequate blood flow.
When cardiac output decreases, the body may divert blood away from the kidneys to preserve the brain and heart.
The result may be:
Decreased urine output
Falling urine output can be an early clue of reduced perfusion.
The textbook divides the vascular system into arteries, arterioles, capillaries, venules, and veins.
Arteries carry blood away from the heart.
They have:
Thick walls
Smooth muscle
Elastic tissue
Higher pressure
Most arteries carry oxygenated blood.
Exception:
Pulmonary artery
Arterioles are small arteries that control blood flow into capillary beds.
They strongly influence vascular resistance.
When arterioles constrict:
Resistance rises.
Blood pressure may increase.
Blood flow to tissues may decrease.
When they dilate:
Resistance falls.
More blood reaches tissues.
Capillaries are microscopic vessels where exchange occurs.
Oxygen and nutrients move:
Blood → tissues
Carbon dioxide and waste move:
Tissues → blood
Capillary walls are extremely thin to permit this exchange.
Veins carry blood toward the heart.
They operate under lower pressure than arteries.
Many contain valves that prevent backward flow.
Skeletal-muscle contraction helps move venous blood upward from the legs.
When venous valves fail, blood may pool and cause:
Varicose veins
Edema
Venous insufficiency
Skin changes
Venous ulcers
Patient findings:
Orthopnea
Fine crackles
Shortness of breath
Low oxygen saturation
Fatigue
Question:
Which side of the heart is most directly associated with these findings?
Answer:
Left-sided dysfunction, because blood is backing up toward the lungs.
Patient findings:
Jugular venous distention
Bilateral leg edema
Abdominal swelling
Weight gain
Question:
Which side is most directly associated?
Answer:
Right-sided dysfunction, because systemic venous blood is backing up.
Findings:
Blood pressure 84/50 mmHg
Cool, clammy skin
Weak pulse
Confusion
Urine output 15 mL/hour
Interpretation:
These findings suggest poor systemic perfusion and reduced cardiac output.
This patient requires immediate evaluation.
Urgent findings include:
New crushing or pressure-like chest discomfort
Chest discomfort with diaphoresis or nausea
Sudden severe shortness of breath
Syncope
New severe palpitations with instability
Very slow or rapid pulse with symptoms
Hypotension with poor perfusion
New confusion
New unilateral weakness
Sudden tearing chest or back pain
New cyanosis
Pulseless extremity
Rapidly worsening pulmonary edema
Routine assessment must stop when the patient appears unstable.
A basic cardiovascular general note might state:
Patient alert and oriented. Skin warm and dry. Heart rate 78/min and regular. Peripheral pulses palpable and equal bilaterally. Capillary refill less than 2 seconds. No jugular venous distention or peripheral edema observed. Patient denies chest discomfort, palpitations, dizziness, and dyspnea at rest.
We will develop full cardiac documentation in later lectures.
Remember:
Pulmonary artery carries deoxygenated blood to the lungs.
Pulmonary veins carry oxygenated blood to the heart.
Valves open and close because of pressure differences.
Systole: ventricular contraction and ejection.
Diastole: ventricular relaxation and filling.
They are associated mainly with valve closure.
Assess mental status, skin, pulses, urine output, and capillary refill.
Use:
Preload = filling.
Contractility = squeeze.
Afterload = resistance.
Which chamber pumps blood into systemic circulation?
A. Right atrium
B. Right ventricle
C. Left atrium
D. Left ventricle
Answer: D
Rationale: The left ventricle pumps oxygenated blood through the aortic valve into the aorta.
Which valve lies between the left atrium and left ventricle?
A. Tricuspid
B. Pulmonic
C. Mitral
D. Aortic
Answer: C
Which vessel carries deoxygenated blood from the heart to the lungs?
A. Pulmonary vein
B. Pulmonary artery
C. Aorta
D. Superior vena cava
Answer: B
What is the normal pacemaker of the heart?
A. AV node
B. Bundle of His
C. Purkinje fibers
D. SA node
Answer: D
Why does the AV node delay the electrical impulse?
A. To close the aortic valve
B. To allow the atria to empty before ventricular contraction
C. To prevent atrial contraction
D. To increase vascular resistance
Answer: B
Which event produces S1?
A. Aortic and pulmonic valve closure
B. Mitral and tricuspid valve closure
C. Mitral and tricuspid valve opening
D. Aortic and pulmonic valve opening
Answer: B
Which statement describes systole?
A. Ventricles relax and fill.
B. Atria receive blood only.
C. Ventricles contract and eject blood.
D. All four valves remain open.
Answer: C
Cardiac output is calculated using which formula?
A. Heart rate ÷ stroke volume
B. Blood pressure × heart rate
C. Heart rate × stroke volume
D. Preload × afterload
Answer: C
Which term describes the resistance the ventricle must overcome to eject blood?
A. Preload
B. Afterload
C. Contractility
D. Automaticity
Answer: B
Which finding most strongly suggests reduced cardiac output?
A. Warm skin and brisk urine output
B. Strong pulses and normal mentation
C. Cool skin, confusion, and decreased urine output
D. Blood pressure 128/76 mmHg with no symptoms
Answer: C
Which finding is more commonly associated with left-sided heart failure?
A. Jugular venous distention
B. Ascites
C. Pulmonary crackles
D. Enlarged leg veins
Answer: C
Which finding is more commonly associated with right-sided heart failure?
A. Pulmonary edema only
B. Peripheral edema and jugular venous distention
C. Isolated headache
D. Dry mucous membranes
Answer: B
Answer without looking back.
Which chambers receive blood?
Which chambers eject blood?
What valve lies between the right atrium and right ventricle?
What valve lies between the left ventricle and aorta?
Which vessel returns oxygenated blood from the lungs?
Which chamber has the thickest wall?
What structure normally starts the heartbeat?
Why does the AV node delay the impulse?
What is systole?
What is diastole?
What causes S1?
What causes S2?
What is cardiac output?
What is preload?
What is afterload?
The atria.
The ventricles.
Tricuspid valve.
Aortic valve.
Pulmonary veins.
Left ventricle.
SA node.
To allow atrial emptying before ventricular contraction.
Ventricular contraction and ejection.
Ventricular relaxation and filling.
Closure of the mitral and tricuspid valves.
Closure of the aortic and pulmonic valves.
Heart rate multiplied by stroke volume.
Ventricular filling and stretch before contraction.
Resistance the ventricle must overcome to eject blood.
Using the blood-flow diagram, trace the complete pathway aloud three times:
Body → vena cavae → right atrium → tricuspid valve → right ventricle → pulmonic valve → pulmonary artery → lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → body
Then draw it from memory.
Next, trace the electrical pathway:
SA node → atria → AV node → Bundle of His → bundle branches → Purkinje fibers → ventricles
Do not memorize the words alone. Explain what happens at each step.
You learned that:
The heart contains four chambers and four major valves.
The right heart sends deoxygenated blood to the lungs.
The left heart sends oxygenated blood to the body.
Valves keep blood moving forward.
The SA node normally initiates the heartbeat.
The AV node delays the impulse so the ventricles can fill.
Systole is ventricular contraction and ejection.
Diastole is ventricular relaxation and filling.
S1 comes from AV valve closure.
S2 comes from semilunar valve closure.
Cardiac output equals heart rate multiplied by stroke volume.
Stroke volume depends on preload, contractility, and afterload.
Left-sided failure commonly produces pulmonary findings.
Right-sided failure commonly produces systemic venous congestion.